There has been significant interest in developing low cost data cards which can be used as a substitute for cash and coins. In many applications such as pay phones, parking meters, vending machines and public transportation, it is convenient to use a data card instead of change for payment. In addition, devices which accept a card are less likely to be vandalized since they do not hold any cash.
To date, the most common form of data card used for this purpose stores information on a magnetic stripe. Information about the value purchased by the consumer can be written onto the stripe. As the card is used in various applications, the data on the card can be updated to reflect the amount which must be debited for the transaction. Thus, these magnetic stripe cards have the attribute that information can be stored and thereafter changed as the monetary value is depleted. The magnetic stripe cards themselves are relatively low in cost to manufacture and are considered disposable.
Magnetic stripe value cards systems do have certain drawbacks. First, the magnetic stripe reader/writers tend to be relatively high in cost and have moving parts. In addition, magnetic stripe reader/writers require significant electrical power to operate and therefore cannot be stand alone devices. Another problem is that the magnetic stripe card does not provide any visual indication of the monetary value left on the card. Finally, the information on a magnetic stripe card can be accidentally erased by stray magnetic fields or could be copied leading to fraud problems.
All of the above drawbacks are overcome with the capacitive data card system of the subject invention. A capacitive-type data card system was previously described by the inventor herein in U.S. Pat. No. 4,280,119 issued Jul. 21, 1981, incorporated herein by reference. In the system described in this patent, the reader included an array of individually addressable primary electrodes and a common secondary electrode (E.sub.ref). A planar data card was provided that included a conductive layer. The data card was "programmed" by including a pattern of holes in the conductive layer which would be in register with the selected primary electrodes of the reader when the card was in place.
In operation, a voltage was selectively applied between the individual primary electrodes and the common secondary electrode of the reader. The conductive body of the data card would be capacitively coupled to the reference ground plane. The capacitance between any particular primary electrode and the secondary electrode (E.sub.ref) would be less if a hole in the card was present at that spatial location of the primary electrode than if the area on the card were conductive. By measuring the detected capacitance adjacent each primary electrode of the reader, the data could be read.
The above described capacitively coupled card system was particularly useful in applications where the data on the card need not be changed. For example, the prior data cards could be used as keys. The cards could be low cost, disposable and the "combination" could be kept hidden. As will be discussed below, the concepts initially disclosed in the U.S. Pat. No. 4,280,119 have now been expanded and enhanced to provide a card where the data can be changed and wherein a visual indication can be provided as to the status of the data on the card.
Accordingly, it is an object of the subject invention to provide a new and improved data storage and retrieval system.
It is a further object of the subject invention to provide a new and improved data storage and retrieval system which is simple and can be manufactured at low cost.
It is another object of the subject invention to provide a new and improved data storage and retrieval system where information on the data card can be read and changed.
It is still a further object of the subject invention to provide a new and improved data storage and retrieval system which has no moving parts.
It is still another object of the subject invention to provide and new and improved data storage system which can operate as a stand alone device with a low power battery source.
It is still another object of the subject invention to provide a new and improved data storage and retrieval system wherein the data bits in one embodiment can be written only once but read many times thereby limiting fraud.
It is still a further object of the subject invention to provide a data card where the data bits in another embodiment can be written and read multiple times.
It is still another object of the subject invention to provide a data card which includes a visual indication of the monetary value remaining on the card.